Firewall Wizards mailing list archives
Re: How automate firewall tests
From: "Paul D. Robertson" <paul () compuwar net>
Date: Mon, 21 Aug 2006 12:10:55 -0400 (EDT)
On Mon, 21 Aug 2006, Patrick M. Hausen wrote:
Hi, Paul!
Hi Patrick!
Blocking ICMP completely breaks PMTUD. Which leads to all sorts of "funny" breakage from the end users point of view.Surely you're in full control of the MTU between your firewall and external router? Letting the border router deal with PMTU isn't necessarily a bad thing.I'm not in control of the MTU along the entire path from server to client. PMTUD is an endpoint mechanism.
Sure, but not many folks are downstream of small MTU serial links anymore, so if you set your external link to frag at 1492 or less (down to the minumum of 576 if you'd like ~100% success,) and allow your router to send ICMP to your server, then you're likely to not to have PMTU issues if you simply don't allow external spoofing of your internal interface.
Or did I get you completely wrong? I'm thinking of e.g. firewall protected public web servers. If you block ICMP, clients that try to access them with a smaller MTU than whatever the server's local interface has got will fail.
But since you control PMTU on your network, you can simply shrink it enough and allow the ICMP traffic between trusted nodes only. Solves the problem. Paul ----------------------------------------------------------------------------- Paul D. Robertson "My statements in this message are personal opinions paul () compuwar net which may have no basis whatsoever in fact." http://fora.compuwar.net Infosec discussion boards _______________________________________________ firewall-wizards mailing list firewall-wizards () listserv icsalabs com https://listserv.icsalabs.com/mailman/listinfo/firewall-wizards
Current thread:
- Re: How automate firewall tests, (continued)
- Re: How automate firewall tests sai (Aug 20)
- Re: How automate firewall tests Dave Piscitello (Aug 30)
- Re: How automate firewall tests Richard Golodner (Aug 18)
- Re: How automate firewall tests Marcus J. Ranum (Aug 20)
- Re: How automate firewall tests StefanDorn (Aug 20)
- Re: How automate firewall tests Strabla Ruggero (Aug 20)
- Re: How automate firewall tests Shahin Ansari (Aug 20)
- Re: How automate firewall tests Patrick M. Hausen (Aug 21)
- Re: How automate firewall tests Paul D. Robertson (Aug 21)
- Re: How automate firewall tests Patrick M. Hausen (Aug 21)
- Re: How automate firewall tests Paul D. Robertson (Aug 21)
- Re: How automate firewall tests Patrick M. Hausen (Aug 21)
- Re: How automate firewall tests Paul D. Robertson (Aug 21)
- Re: How automate firewall tests Oliver Humpage (Aug 21)
- Re: How automate firewall tests Marcus J. Ranum (Aug 21)
- Re: How automate firewall tests Isaac Van Name (Aug 21)
- Re: How automate firewall tests Shahin Ansari (Aug 20)
- Re: How automate firewall tests Avishai Wool (Aug 22)